1. Technical Field
The present invention relates to a vehicle control apparatus and a method for controlling a vehicle.
2. Related Art
In recent years, research and development has been conducted concerning techniques for providing assistance in a turn of a vehicle. Examples of such techniques include a technique of controlling braking or driving forces (hereinafter referred to also as “braking/driving forces”) of wheels to perform turn control on the vehicle.
Japanese Unexamined Patent Application Publication (JP-A) No. 2011-254590, for example, discloses a technique of controlling braking/driving forces of motors of an electric vehicle so as to make a turning acceleration have a value in accordance with a steering wheel angle, while preventing a slip ratio of each wheel from exceeding a predetermined value.
JP-A No. 2010-119204, for example, discloses a technique, related to a vehicle control apparatus, of varying a control longitudinal force for each wheel in accordance with a steering characteristic determined from an actual yaw moment.
The techniques disclosed in JP-A No. 2011-254590 and JP-A No. 2010-119204, however, have a problem in that an improvement in turning performance of the vehicle and an improvement in stability of the behavior of the vehicle cannot be easily achieved at the same time.
For example, in the case where a parameter for turn control is set in accordance with a high value of a road surface friction coefficient (hereinafter referred to also as “μ”), oversteer occurs more easily and, as a result, the vehicle spins more easily than in the case where this parameter is set in accordance with a low value of μ, when the vehicle is traveling on a low μ road surface.
Conversely, in the case where the parameter for the turn control is set in accordance with a low value of μ, turning performance of the vehicle is reduced compared to the case where this parameter is set in accordance with a high value of μ, when the vehicle is traveling on a high μ road surface.